This invention relates to a method for continuous monitoring of patients to detect the potential onset of sepsis.
Sepsis is a medical condition in which bacteria invade the body causing a serious infection. Large and increasing numbers of microorganisms overwhelm the body's defense systems and actively multiply in the bloodstream. Sepsis is associated with a large stress on the body, such as trauma.
Over 684,000 cases of sepsis were reported in the United States in 1998. The mortality rate for these cases was 17.4%. Overall, sepsis is the 11th leading cause of death in the U.S. and the annual cost of providing care for this condition is approximately $15 billion.
Sepsis is almost always accompanied by an increase or decrease in body core temperature as well as elevation in pulse and respiration rates.
Current hospital care protocols for detecting onset of sepsis require periodic body temperature, pulse rate, and respiration rate monitoring, and patient observation. A typical sepsis screening criterion used by healthcare providers is as follows:                a. Body core temperature greater than 38.3° C. (about 101° F.) or less than 35.6° C. (about 96° F.).        b. Heart rate greater than 90 beats per minute.        c. Respiration rate greater than 20 respirations per minute.        d. Clinical evidence of infection, such as redness around an infection site, swelling, or facial pallor.        
The presence of any two of these four factors is considered to be an indication of the potential onset of sepsis, rendering further patient evaluation, including blood cultures and chest x-rays, desirable. If the further evaluation confirms the diagnosis of sepsis, the accepted clinical treatment is the administration of substantial doses of intravenous antibiotics.
Early detection of sepsis and appropriate administration of antibiotics can greatly reduce the mortality rate of this disease.
For a patient who has not been admitted to a critical care unit or intensive care unit, the intervals at which body temperature, heart rate and respiration rate are measured during hospitalization can be quite long and quite variable and may depend on circumstances other than the current condition of the patient, such as the workload of nurses and other healthcare professionals.
It can be appreciated that more frequent body temperature, heart rate and respiration rate monitoring could be helpful in detecting the possible onset of sepsis so that a rapid diagnosis and immediate care can be provided to thwart this disease from rapidly overwhelming the patient's immune system.
U.S. patent application Ser. No. 10/017,098 discloses a digital sensor for a miniature medical thermometer and body temperature monitor. This digital sensor can be implemented in a pill that can be ingested for measuring body core temperature, in a small skin patch for measuring skin temperature, or in a capsule that can be placed in a body orifice, such as the ear canal.
U.S. patent application Ser. No. 10/071,534 discloses a skin patch including a telesensor for emitting a signal that represents a physiological parameter sensed by the telesensor. The physiological parameters that can be sensed by an appropriate telesensor include body temperature and ECG voltage. It is known that heart rate and respiration rate can be derived from the ECG voltage waveform.